Fixture for making honeycomb panel



1965 H. R. HERMAN ETAL 3,

FIXTURE FOR MAKING HONEYCOMB PANEL Original Filed Nov. 26, 1954 4 Sheets-Sheet l INVENTORS.

H. R. HERMAN BY 5. R. ALSOBROOK 1965 H. R. HERMAN ETAL 3,170,428

FIXTURE FOR MAKING HONEIYCOMB PANEL Original Filed Nov. 26, 1954 I 4 S eets-Sheet 2 INVENTORS.

H. R. HERMAN BY 8. R. ALSOBROOK ATTORNEY 23, 1965 H. R. HERMAN ETA L 3,170,428

FIXTURE FOR MAKING HONEYCOMB PANEL Original Filed Nov. 26, 1954 4 Sheets-Sheet 3 F I G. 5

I NVENTORS.

H. R. HERMAN W BY 8. R. ALSOBROOK ATTRNEY 1965 H. R. HERMAN ETAL 7 FIXTURE FOR MAKING HONEYCOMB PANEL.

Original Filed Nov. 26, 1954 4 Sheets-Sheet 4 7 INVENTORS. VACUUM F! H. R. HERMAN SOURCE BY B. R. ALSOBROOK w gm.

1 ATTORNEY United States Patent 3,170,428 FIXTURE FOR MAKING HONEYCOMB PANEL Hartley R. Herman, La Mesa, and Benjamin R. Alsobrook, Chula Vista, Califi, assignors to Rohr Corporation, a corporation of California Original application Nov. 26, 1954, Ser. No. 471,394, pow Patent No. 2,944,504, dated July 12, 1960. Divided and this application July 11, 1960, Ser. No. 48,783

7 Claims. (Cl. 113-991) This application is a division of our copending application for Fixture for Making Honeycomb Panel, Serial No.

471,394, filed November 26, 1954, now Patent No. 2,94-4,-

504, granted July 12, 1960.

This invention relates to a panel structure of sandwich type in which thin metal shaped somewhat like a honeycomb is secured between two enclosing skins and to the apparatus and method use for fabricating such panel.

An object of the invention is to provide a fixture for holding the sandwich structure while its components are being brazed together which is capable of heating and cooling with the sandwich with a minimum amount of distortion.

Another object is to provide a holding fixture made up of a number of small individual components so connected together that it will remain rigid and hold its contour even when repeatedly heated to a temperature of about small amount of heat to be supplied to it to raise its temperature to that required for brazing the sandwich components together.

Another object is to provide means for stiffening the lattice structure and preventing one portion of it from shifting with reference to other portions in addition to the rigidity provided by the contact of the lattice strips with each other. This additional stifiening means is preferably perforated to permit the free flow of gas therethrough for securing a more uniform heating.

A further object is to provide for a small amount of slippage of the sandwich with reference to the fixture by means of a thin sheet interposed between them, there by preventing warpage and change in the sandwich contour as it cools after brazing.

Another object is to provide means between the supporting lattice andsandwich to prevent the concentration of pressure in narrow areas of the sandwich and assure a more uniform pressure distribution over the sandwich before and during the brazing.

In cases where the sandwich has a convex contour, a further object is to provide a thin metal sheet enveloping the sandwich and arranged to apply substantially uniform pressure to the various portions thereof, the thickness and material of the sheet preferably being such that the sheet cools at substantially the same rate as the sandwich.

Another object is to provide for the heating and brazing of the metal sandwich in a reducing or inert gas which will not form undesirable compounds of the metals such as those due to oxidation or carburization.

A still further object is to provide for the preheating of the sandwich assembly prior to brazing in a muffle not much larger than it to a temperature somewhat below the brazing temperature and to complete the brazing in a high ice temperature furnace in which the muffle and sandwich are placed, the furnace being heated bya suitable heating means to a temperature above the brazing temperature.

Another object is to provide such a mufile which will distribute the heat received from the source of furnace heat and prevent the heat rays from such source from directly impinging on the sandwich and thereby causing uneven heating thereof.

A further object is to provide for the slow, uniform cooling of the brazed sandwich by removing the mufiie from the furnace and permitting the sandwich to remain in the muffle while cooling. This procedure prevents the cool ambient air from reaching the sandwich with resultant uneven cooling thereof. 1.

Another object is to provide means for supporting the muflle out of contact with the furnace to permit free circulation of the furnace gases around the mufiie thereby insuring its more even heating than if it rested on the furnace floor. i

A further object is to provide a clamping structure for drawing an enveloping sheet against the sandwich in which an increase in clamping pressure is effected due to the difference in the coefiicients of expansion of components of the clamping device. This arrangement compensates for the expansion of the enveloping sheet due to the large rise in temperature and holds it firm against the sandwich.

Further objects will become apparent as the description proceeds. For a better understanding of the invention reference is made to the accompanying drawings, in which: a

FIG. 1 is a perspective view of a honeycomb sandwich embodying the invention;

FIG. 1A is a detail view of a portionof the honey comb;

FIG. 2 is a perspective view of a holding fixture containing the sandwich of FIG. 1;

FIGS. 3 and 4 are views of lattice strips used in the fixture of FIG. 2; a

FIG. 5 is a view partly in section and partly diagrammatic of a honeycomb sandwich and mufile in a furnace;

FIG. 6 is a perspective view showing a holding fixture containing a sandwich panel, and

FIG. 7 is a sectional View on line 7-7 of FIG. 6.

Referring to FIGS. 1 and 2 the invention is illustrated in connection with the construction of a honeycomb sandwich 15 having a central core composed of diamond shaped cells 16 which are connected together by welding or other known means, the outer ends of the cells being brazed to a covering skin 17 and their inner ends brazed to a concave shaped skin 18, the skin 18 terminating in straight edges 19 to which are brazed the ends of a pair of inwardly curved flanges 20, 21. The lower ends 22 of skin 17 are also straight and have brazed thereto outwardly curved flanges 23, 24 of the shape shown. All the above parts are preferably made of stainless steel which has high tensile strength and although the thickness of the metal composing the honeycomb cells may be only from 1 to 3 thousandths of an inch, nevertheless when the parts of the sandwich are brazed together the resulting structure has great strength and strongly resists torsion and bending. Prior to brazing, in a manner to be later described, the flanges, 20, 21 are tack welded at Patented Feb. 23, 1965 comprises a horizontal base 27 in the. form of a lattice composed of a plurality of longitudinal strips 28 interlocked with a plurality of transverse strips 29. Each strip23 has a series of equally spaced apart slots 30 and a set of holes 31 therethrough and eachstrip 29 has a series of equally spaced apart slots 32 and a set of holes 33 'therethrough, as shown in FIGS. '3 and 4. By as- I sembling the strips together so that the unslotted portion and .040" thick and made of stainless steel.- Elongated clamp jaws 52 are pressed against the lower ends of sheet Slby means of a series of bolts or screws 53 thread ed in spaced apart similar supports 54. The face of jaw 54 which presses against sheet 51 is serrated or otherwise roughened to give a better 'grip and is contoured to the shape of flange 24. Each support 54 is attaChed to lattice within the desired tolerance, .it may be made fiat within a tolerance of .001 inch by grinding. The top face, of the lattice serves as a horizontal reference or datum plane of the fixture. The strips 28 and 29am preferably composed of a steel alloy capable of standing high temperatures without appreciable.distortionand maybe about sandwich to the peripheral contour of the lattice com prising the formers and strips 39, the assembly is .062 inchthick when the strips composing the lattice are 1 inch apart. The holesSl, 33 permit hot gas to circulate through the lattice structure promoting its 'more rapid heating and more uniform temperature. Attached base 27 preferably by a bolt (not shown) which passes through the lattice and enters a threaded hole in the bottom of the support. All the supports together with their adjusting screwsare thus readily removed from the lattice. Supports 54 may be made of Invar alloy and screws 53 of metal which has a substantially higher coefiicient of expansion than Invar so that as the temperature increases during'the brazing, the screws exert a somewhat v greater pressure on jaws 52 which in turn keep enveloping sheet 51 tightly pressed against the outer skin 17 of the sandwich notwithstanding theincrease in length of sheet 51 between jaws 52 due to increase in temperature;

After sheet 51 has been drawntight to conform the placedin a stainless steel enclosing muffle55 (FIG. 5) which is substantially airtight, with the angles 34 resting on the floor 56 of the muffle. A stream of argon gas is then passed into the muffle to purge it of air and a stream to the bottom of the lattice are a set of angle irons 34, 1

angles and lattice permits the free circulation of hot gases therethrough to assist in the rapid heating of the fixture and a more uniform temperature distribution.

of hydrogen ,gas then passed into it until the muffle and honeycomb are completely filled with hydrogen. sandwich and rnufiie'are'then preheated by any suitable heating means to a temperature of about500 F., the heater illustrated consisting'of two Calrodelectric heaters 57 supplied-with current from the usual A.C. source (not ,shown)., Itwill be understood that more than two heaters may be used, if desired. This heating partly purges A plurality of similar formers 35 have flat edges seated on lattice 27, each former preferably being composed of'a plurality of annular segments secured together by bolts 37, as shown. Deep slots 38 are cut in the periphery of each former and longitudinally extending thin strips 39 are seated in these slots so that the several formers are in alignment and parallel to each other. Each former is secured in place to lattice 27 by bolts 40 which pass through a pair of angle irons 41 which are welded or otherwise secured to lattice 27. Near its base each former terminates in a vertical edge 42, against which rests the vertical edge of former extension 43 whose upper end 44 engages the end of the honeycomb sandwich and whose curved edges 45, 46 fit against flanges 20, 24 respectively and flanges 21, 23. After assembling the formers 35 and lattice strips 39, if their outer edges do not exactly conform to the desired shape, the outsideperiphery of the assembly is ground or otherwise machinedsprayed onto the resin coating. Before placing the assembled prepared sandwich in the brazing fixture, a stainless steel sheet 50 having a thickness of about .020" is laid on the curved periphery of the fixture to cover all the formers and strips 39 and the assembled sandwich then placed in position, as shown in FIG. 2. The former extensions 43 are then put in place and an enveloping sheet 51 of stainless steel draped over the sandwich and the flanges 23, 24. Sheet v51 preferably is between .030

the rnufile and assures the removal of all moisture there- 7 from.

' After preheating in the mufile, the mufile and, sandwich are placed ina high temperature furnace 58, the muffie being supported above the floor 59 of the furnace by a plurality of angle irons 60 arranged to provide open spaces 61 through which the furnace gases may circulate to accomplish more uniform heating. The furnace walls are preferably lined with fire brick (not shown) in a known manner. The furnace may be heated by a plurality of electric heaters 62 diagrammatically shown or by hot combustion gases supplied from a burner (not shown), the temperature in the. furnace being maintained from 150 to 200 F. above the melting point of the brazing alloy. An inert gas as, for example, hydrogen which will not oxidize or otherwise form compounds with the metal of sandwich 15 is introduced into a metal heating coil 63 in the furnace, the outlet of the coildischarging'the hot gas against a baflle 64 in themuifle, the bafile having discharge outlets 65 which serve to direct the hot inert gas along the wall of the muffle and thus prevent it from impinging directly on the sandwich with resultant uneven heating thereof.

As soon as the furnace door (not shown) is closed, the inert gas is passed through coil 63 to heat. it, the gas leaving through a pipe 66. Soon after the sandwich and interior of the muflie have reached the brazing temperature, as indicated by one or more pyrometers (not shown), having their. terminalsin the muffle, the gas supply to pipe 63 is shut off and the mufile removed from the furnace and allowed to cool in the ambient air with the fixture 26 and the brazed sandwich therein. While cooling, another hydrogen supply is connected to supply gas into the mufie against baffle 64, the hydrogenbeing supplied until the sandwich cools down to about 800 F., and serving to prevent oxidation of the sandwich. The hydrogen supplyis then stopped andargon supplied in- 'stead, argon being admitted to .the mufiie until it has reached normal room temperature. The argon supply is then shut off and the'cooled fixture and sandwich removed from the mufile.

The.

E a? While one muffle is cooling, another preheated one with its contained sandwich may be placed in the furnace section 93 of the fixture has intersecting lattice strips 94 p of thetype above descgibed, the lower edges of which rest on a perforated plate 95 whose lower face is ground to the contour of the desired sandwich 96. Plate 95 rests on the upper skin 17 which is to be brazed to the upper end of cells 16. The skin 18 to be brazed to thelower end of the cells rests on perforated plate 97 whose top face is ground to the curved contour of sandwich 96. The bottom section 98 of the fixture is airtight and may be connected to a vacuum pump99 by a valve 100. Bottom section 98 has attached thereto a vertical plate 101 (FIG. 6) which carries a channel 102 in which is disposed a continuous mass of sealant material 103. Upperfixture section 93 has hermetically secured thereto a rectangular hollow casing 104 having vertical side and end wall 105 which extend into the sealant 103. Upper section 93 is guided by a set of vertical pins 106 whose lower ends are secured to brackets 107 which in turn are attached to the sidewall of fixture section 98. Wall 105 has attached to it a set of plates 108 drilled to receive and slide along the pins 106, the latter being slotted to receive the wedges 109. Surrounding the pins 106 aresleeves 110 whose length is such that they take the weight of the fixture sec- .tion 93' and prevent its weight from bearing on sandwich 96. A pair of Z shaped bars 111 extend along the entire side edges of core 16 and are brazed thereto, the webs of these bars being pressed against the'core by a plurality of screws 112 spaced about 6 inches apart. The screws 112 are threaded into supports 113 which are attached to the sides of plate 97 by bolts 114. The sides of the panel are thus maintained to the required dimensions.

' The brazing material having been applied to the top of sheet 18 and bottom of sheet 17 and to those faces of Z bars 111 which contactthe sandwich panel, the panel is placed in the fixture, the top portion 93 of the fixture lowered into position and the screws 112 adjusted. The fixture is then purged with argon gas and placed in a brazing furnace of the type above described. Valve 100 is then opened to apply vacuum to the interior of fixture section 98 and the bottom face of skin 18, thereby drawing this skin into contact with plate 97 and causing it to conform to the contour of its top face. Simultaneously dry hydrogen gas under pressure is conducted into hollow casing 104 by a pipe 115 leading from a tank 116 of dry hydrogen gas. This gas reaches the top face of skin 17 and presses the skin firmly against core 16 and causes the core to conform to the contour of its bottom skin 18 so that the entire panel has the desired size and contour prior to reaching the brazing temperature in the furnace and during the brazing. When the brazing is complete, the fixture and panel are removed from the furnace and the vacuum maintained under sheet 18 and the hydrogen pressure over sheet 17, until the parts have cooled to about 800 F. when the entire fixture is purged with argon gas and the brazed panel removed therefrom.

In each of the illustrated examples, in order to prevent the accidental brazing of the fixture to the honeycomb panel, those parts of the fixture which contact the panel are covered with a thin coating of chromium oxide or aluminum oxide (A1 0 The entire fixture may be plated with chromium in a known manner and the plated fixture then heated in an oxidizing atmosphere to convert the plating to chromium oxide.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment of the'invention is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Having thus described the invention, what we claim as new and useful and desire to secure by Letters Patent 1. A lattice fixture adapted to support a honeycomb sandwich composed of a cellular core, afirst skin in contact with the lower end of said core and a second skin in contact with the upper end of said core while the skins are brazed'to the core, said fixture comprising a first set of spaced apart thin metal strips; a second set of spaced apart thin metal strips transverse to and interlocked with r the strips of said first set; said strips of both sets having the bottom edges thereof disposed in a common plane; a rigid plate secured to the top edges of a plurality of the strips-of both sets, the top face of said plate being shaped to the contour to which the sandwich is deformed in response to the application of pressure to the top face of said second skin; and at least one rigid elongated member secured at the center only thereof to the bottom edges of the lattice comprising the strips of both sets to support the same and to restrain the strips from shifting.

2. Means for deforming a honeycomb sandwich disposed between two sections of a fixture to a desired contour preparatoryto brazing the sandwich, comprising a lower fixture section comprising a plurality of intersecting thin metal strips interlocked together to provide a lattice, a concave plate secured to the upper end of said lattice, said plate having a plurality of spaced apart holes extending therethrough; means for decreasing the pressure within said holes simultaneously to draw the sandwich against said concave plate; an upper fixture section comprising a plurality of intersecting thin metal strips interlocked together to provide a second lattice; a convex plate secured to the lower end of said second lattice, the curvature of said convex plate being complemental to that of said concave plate, said convex plate having a'plurality of spaced apart holes extending therethrough; and means for increasing the pressure within said last named holes simultaneously to press the sandwich against said concave plate.

3. A lattice fixture comprising a first set of parallel thin metal strips provided with narrow slots terminating in the top edge of the strips; a second set of parallel thin metal strips whose thickness is substantially equal to the width of said-slots, the strips of said second set having a plurality of narrow slots terminating in the bottom edge thereof, the unslotted top portion of the strips of the second set extending for a substantial distance into the slots of said first set of strips; said strips of both sets having the bottom edges thereof disposed in a common plane; at least one rigid elongated member secured at the center only thereof to the bottom edges of the lattice comprising the strips of both sets to restrain the strips from shifting; the top edges of all said strips being shaped to provide the desired contour for a member while held against said top edges during heat treatment, the mass of said fixture being relatively small whereby it will heat rapidly during the heat treatment.

4. A lattice fixture adapted to support a honeycomb panel for brazing, said panel comprising a core of connected metal cells; a first metal skin under the end of said cells; brazing alloy between the top of said skin and said cells; a second metal skin over said cells; brazing alloy between said cells and second skin; said lattice fixture comprising a first set of parellel thin metal strips; a second set of parallel thin metal strips interlocked with the strips of the first set and disposed transversely with respect thereto, the top edges of all said strips being shaped to provide the desired supporting surface for the honeycomb panel during brazing, the top edges of all said strips defining a convex contour of the panel; means for pressing said second skin toward said core and simultaneously pressing said first skin against the top edges of said strips preparatory to heating said panel and fixture to effect the brazing, said means comprising a thin sheet of metal unattached to said second skin and overlying said second skin for pulling said second skin toward said core whereby slippage between said thin metal sheet and second skin may occur due to their unequal expansion upon heating, and at least one rigid elongated member secured at the center only thereof to the bottom edges of the lattice comprising the strips of both sets to support the same and to restrain the strips from shifting.

5. A lattice fixture adapted to support a honeycomb sandwich composed of a cellular core, a first skin in contact with the lower end of said core and a second skin in contact with the upper end of said core while the skins are brazed to the core, said fixture comprising a first set of spaced apart thin metal strips; a second set of spaced apart thin metal strips transverse to and interlocked with the strips of said first set; said strips of both sets having the bottom edges thereof disposed in a common plane; at least one rigid elongated member secured at the center only thereof to the bottom edges of the lattice comprising the strips of both sets to support the same while also providing for relative expansion and contraction of the lattice and elongated member in response to the brazing heat; a rigid plate secured to the top edges of a plurality of the strips'of both sets, the top face of said plate being shaped to the contour to which the sandwich is deformed in response to the application of pressure to the top face of said second skin, said rigid plate having a plurality of spaced apart openings extending therethrough; and means for decreasing the pressure within said openings to thereby draw the bottom face of said first skin tightly against the top face of said plate.

6. A lattice fixture adapted to support a honeycomb sandwich composed of a cellular core, a first skin in contact with the lower end of said core and a second skin in contact with the upper end of said core while the skins are brazed to the core, said fixture comprising a first set of spaced apart thin metal strips; a second set of spaced apart thin metal strips transverse to and interlocked with the strips of said first set; a rigid plate secured to the top edges of a plurality of the strips of both sets, the top face of said plate being shaped to the contour to which the sandwich is deformed in response to the application of pressure to the top face of the said second skin; a rigid member disposed in contact with substantially the entire top face of said second skin, said rigid member having a plurality of spaced apart openings extending therethrough; and means for increasing the pressure within said openings to thereby press said second skin against said cellular core.

7. A lattice fixture adapted to support a honeycomb panel for brazing, said panel comprising a core of connected metal cells, a first metal skin under the end of said cells, brazing alloy between the top of said skin and said cells, a second metal skin over said cells, and brazing alloy between said cells and said skin; said lattice fixture comprising a first set of parallel thin metal strips; 21 second set of parallel thin metal strips interlocked with the strips of the first set and disposed transversely with respect thereto, the top edges of all said strips being shaped to provide the desired supporting surface for the honeycomb panel during brazing; means defining a desired contour for said core interposed between said first skin and said supporting surface; means for pressing said second skin toward said core and simultaneously pressing said first skin against said contour means preparatory to heating said panel and fixture to effect the brazing; said strips of both sets having the bottom edges thereof disposed in a common plane; and at least one rigid elongated member secured at the center only thereof to the bottom edges of the lattice comprising the strips of both sets to support the same and to restrain the strips from shifting.

References Cited by the Examiner UNITED STATES PATENTS 1,272,809 7/18 Johnson 29475 1,873,053 8/32 Shaw 338--316 XR 2,366,935 1/45 Schmid.

2,384,303 9/45 Heath 21958 XR 2,385,352 9/45 Davis.

2,394,479 2/46 Priessman 338316 XR 2,445,801 7/48 Partiot 29-455 2,462,607 2/49 Browne 338-316 XR 2,634,697 4/53 Nofzinger 113-99 2,654,686 10/53 Hansen 29*455 2,700, 632 1/55 Ackerlind.

CHARLES W. LANHAM, Primary Examiner.

WHITMORE A. WILTZ, JOHN F. CAMPBELL,

' Examiners. 

1. A LATTICE FIXTURE ADAPTED TO SUPPORT A HONEYCOMB SANDWICH COMPOSED OF A CELLULAR CORE, A FIRST SKIN IN CONTACT WITH THE LOWER END OF SAID CORE WHILE THE SKINS IN CONTACT WITH THE UPPER END OF SAID CORE WHILE THE SKINS ARE BRAZED TO THE CORE, SAID FIXTURE COMPRISING A FIRST SET OF SPACED APART THIN METAL STRIPS; A SECOND SET OF SPACED APART THIN METAL STRIPS TRANSVERSE TO AND INTERLOCKED WITH THE STRIPS OF SAID FIRST SET; SAID STRIPS OF BOTH SETS HAVING THE BOTTOM EDGES THEREOF DISPOSED IN A COMMON PLANE; A RIGID PLATE SECURED TO THE TOP EDGES TO A PLURALITY OF THE STRIPS OF BOTH SETS, THE TOP FACE OF SAID PLATE BEING SHAPED TO THE CONTOUR TO WHICH THE SANDWICH IS DEFORMED IN RESPONSE TO THE APPLICATION OF PRESSURE TO THE TOP FACE OF SAID SECOND SKIN; AND AT LEAST ONE RIGID ELONGATED MEMBER SECURED AT THE CENTER ONLY THEREOF TO THE BOTTOM EDGES OF THE LATTICE COMPRISING THE STRIPS OF BOTH SETS TO SUPPORT THE SAME AND TO RESTRAIN THE STRIPS FROM SHIFTING. 